The present invention is directed to new and useful improvements in sedimentation apparatus and in particular to skimmer mechanisms for clarifiers or thickeners utilizing rotary rake type settling tanks.
Settling tanks utlizing rotary rake mechanisms are well known for use in the separation of solids from a liquid suspension such as in waste water or sewage treatment wherein solids are settled to the tank bottom. A central rotary rake structure is provided for raking the sludge or other solids that settle from the suspension to a central sump outlet located in the tank bottom while the supernatant or clarified liquid is removed at an overflow launder at the upper peripheral boundary of the tank.
In the treatment of certain suspensions very light solids float to the top of the liquid and form a scum on the surface thereof which must be removed. In the past there have been many types of skimming devices proposed or employed for removing this floating material such as surface conveyers or rotating skimmer blades which move the floating material to appropriate traps or boxes. Such latter type mechanisms are disclosed for example in U.S. Pat. No. 3,919,090 or U.S. Pat. No. 4,341,643 wherein rotating skimmer arms having a scum remover at one end thereof are provided to sweep across the upper surface of the liquid level in a settling tank to move the scum up an inclined surface into a scum discharge box. A similar type skimmer is also disclosed in U.S. Pat. No. 2,822,928 which discloses a skimmer arm and blade which are rotated about the upper surface of the liquid in the clarifier. The blade is provided with a squeegee surface for sweeping the floating scum matter up a ramp into a discharge box. Prior art patents such as U.S. Pat. No. 2,124,284 or U.S. Pat. No. 2,880,876 utilize endless belt type conveyer devices at the upper surface of the liquid for removing the floating layer from the liquids.
Although the skimmer devices of these prior disclosures may have proven effective for their intended purposes they are of a generally complex construction increasing the requirements of the main rake and drive structure supporting the same and are generally not effective throughout the entire diameter of the settling tank for insuring a clean sweeping movement of the floating material to a discharge point at the periphery or other point of discharge in the settling tank.
It is the object of the present invention to provide a novel skimmer means for settling tank that provides for a full diameter sweep across the surface of the liquid.
Another object is to provide a novel skimmer and discharge collector without the use of ramps or other similar complex mechanisms within the tank.
A further object is to provide a novel means for effecting a full radius sweep of an individual skimmer arm to a discharge point at the periphery of the tank and including means for automatically restoring the skimmer to an operative sweeping position after removal of the floating maerial.